A headlight, especially for motor vehicles, contains at least one optical system comprising a powerful light source and optical elements. The light source emits light rays and the optical elements represent a system of refractive and reflective surfaces, interfaces of optical environments and diaphragms that influence the direction of light rays within the creation of the output light trace.
In modern headlights, projector systems are frequently used comprising light units adapted to amplify light by stimulated emission of radiation, called laser units. A laser is used in headlights as an optical source of electromagnetic radiation in the form of light-emitting diodes. Diodes use the principle of electroluminescence, when after the introduction of electric voltage, electric energy is transformed into light in the place of P-N transition. This light is emitted from the laser diode as coherent and monochromatic. Light emitted by laser diodes most frequently has the blue color so to be used in car headlights, light rays pass through a converter, generally in the form of yellow phosphorus, e.g. Cr:YAG, which turns blue light to white light.
Thus, laser diodes may be used, unlike common LED's, in applications where a sharply directional light beam needs to be created. Light devices are known from the documents US20110280032A1, WO2015140001A1, US20150043233A1, and WO2014121315A1, wherein laser diodes make it possible to exactly focus light rays in a particular direction and to hit even a very distant point, which is used to ensure the high-beam light function in headlights of motor vehicles. In accordance with valid regulations, light may be emitted up to the distance of 600 m in front of the vehicle. Thanks to up to 80% higher efficiency of optical systems designed for laser sources, a higher performance of headlights can be achieved. Luminance of a laser source can be up to 100 times higher, while optical systems comprising a laser diode feature 50% lower energy consumption compared to conventional LED's. A disadvantage of most current laser optical concepts is the fact that the benefits of laser diodes are generally used for the high beam function where a high-intensity light trace needs to be provided, the above mentioned laser systems not being adapted for changes of the light characteristic of the output light beam depending on the conditions where the vehicle is found, e.g. no dazzling of the oncoming driver, width of the light beam based on the vehicle speed, the emission direction of the light beam based on the steering wheel position, etc.
Another disadvantage of laser as well as LED optical concepts is the fact that excessive light intensity may harm vision, and the headlights of vehicles must be fitted with safety elements to avoid exceeding of safety limits, especially in case of damage of converter substances or the entire laser diodes. Safety elements for laser beam emission are described e.g. in the documents WO2014072227A1, EP2821692A1, WO2015049048A1, WO2012076296A3, and U.S. Pat. No. 8,502,695B2.
A solution is known from the document EP2954256B1, wherein the light characteristic of the output light beam is ensured by at least two laser diodes when individual modulated laser rays are directed to a light converter by means of turning of a micro-mirror. A disadvantage of this solution is the fact that the projected light image consists of several segments, a laser diode being associated with each segment, which makes the optical concept relatively costly and optically inefficient.
From the prior art, diffraction dividers of the laser beam are known that consist of a binary grating that is designed in such a way to divide coherent light emitted from the laser diode to a particular number of light streams. From the documents US20140307457 and CZ20150890, lamps are known where the light emitted by one laser diode is divided by a divider to a higher number of partial rays. The divider works as a router of photons to direct photons to a pre-defined space. A disadvantage of the prior art is the fact that optical systems comprising a laser beam divider are intended for signal functions, and are not adapted to create the required output characteristics for lighting of the carriageway in front of the driver. Another disadvantage is the fact that the micro-mirror only turns around one axis, which means that the resulting image can only be influenced in one direction and thus only a light stripe can be produced by each laser diode.
A solution is known from the document U.S. Pat. No. 4,868,721 that contains an assembly of rotary/oscillating micro-mirrors that makes it possible to influence the resulting image in two directions. Between the laser diode and the mirror, a light modulator is situated making it possible to influence the light characteristics of the laser beams of rays, or to even entirely interrupt the laser beam of rays. A disadvantage of this design is the fact that the modulator influences the light beam before it hits the micro-mirror, which means that the light characteristic of the light beam after the reflection from the micro-mirror cannot be influenced.
The document US20130058114 discloses a design wherein light rays reflected by an array of micro-mirrors are directed through an optical assembly comprising diffraction elements in the form of lenses and prisms, which makes it possible to produce a light image consisting of a few segments of different shapes, while different light characteristics can be achieved in each segment. A disadvantage of this design is the fact that an asymmetrically composed light image cannot be created and the light characteristic of the output light trace cannot be dynamically influenced, e.g. an unlit part inside one segment of the resulting light image cannot be created.
More laser optical systems are known from the documents DE19907943, EP2063170, DE102008022795, DE102011080559A1, and EP2990264, that are equipped with micro-mirrors or with opto-electro-mechanical systems called MOEMS. Opto-electro-mechanical elements generally consist of an array of small mirrors that nowadays enable, on the micrometer level, direct control, routing and shaping of light before the light falls onto the converter of the laser beam of rays. A disadvantage of existing laser concepts is the fact that rotation/oscillation of micro-mirrors is carried out in a resonance manner when the micro-mirror oscillates at the same frequency and amplitude, and if the shape of the output light image needs to be influenced, the laser source of light must be switched off. It is not possible to stop a micro-mirror in a certain position or offset/shift the rotation/oscillation axis either. The speed of the micro-mirror is variable because when the rotation direction is changed, the micro-mirror speed is reduced. This results in uneven distribution of the intensity of light. To achieve even distribution of the intensity of light, the laser ray or the beam of laser rays must be switched off, switched on or modulated at a certain time.
The documents US2004227984 and U.S. Pat. No. 7,428,353 disclose technical designs of MOEMS controlling the micro-mirror rotation/tilt angle, the micro-mirror oscillation range/angle, oscillation rate and frequency through electric or electromagnetic control signals, while micro-mirror oscillation can be implemented in two mutually independent directions.
The object of the present invention is to remedy the above-mentioned drawbacks of the prior art and to enable dynamic changing of the light characteristics of the output light beam of a light device, especially the projector system of a headlight for motor vehicles equipped with a laser diode, depending on the conditions where the vehicle is found. The output light trace must comprise at least one light pattern, while the light characteristics of individual patterns must be created from one laser diode in such a way that it is switched off to a minimal extent. The entire optical system must be optically efficient with low production demands.